ERIN R. PASTER, DVM 1,2 , DARRYL N. BIERY, DVM, Diplomate ACVR 1,2 , DENNIS F. LAWLER, DVM 1,2 , RICHARD H. EVANS, DVM, MS 1,2 , RICHARD D. KEALY, PhD 1,2 , THOMAS P. GREGOR, MS 1,2 , PAMELA J. McKELVIE, VMD 1,2 , and GAIL K. SMITH, VMD, PhD 1,2 Department of Clinical Studies—Philadelphia, School of Veterinary Medicine, University of Pennsylvania, Philadelphia PA; 2 Nestle Research Center, St Louis, MO; and Veterinary Pathology Services, Aliso Viejo, Vet Surg 2009 Feb 38 2 169-172 ABSTRACT Objective—To longitudinally characterize the radiographic appearance of un-united medial epicondyle (UME) of the humerus, evaluate UME association with osteoarthritis (OA) and consider its relevance to the elbow dysplasia complex. Study Design—Longitudinal cohort study. Animals—Labrador retrievers (n=48) from 7 litters. Methods—Forty-eight same-sex littermates were paired for this lifetime feeding study. One of each pair was control-fed; the pair mate was fed 25% less than the control each day. Elbows of 46 surviving dogs were radiographed at ages 6 and 8 years, and/or at end-of-life (EOL). Elbow histopathology was done EOL, although UME lesions were not evaluated histologically. Results—Seven dogs (15%) had UME, representing 5 litters; 4 were control-fed, 3 diet-restricted. Six (86%) dogs had unilateral lesions; 1 was bilateral. UME was evident on craniocaudal (CrCd) radiographic projections by 8 years in all dogs. UME was detected in only 1 elbow by mediolateral radiographic projection. Elbow OA frequency in UME affected dogs was not significantly different from the remaining study population. Histopathologic lesions were bilateral in dogs with unilateral UME. Conclusions—UME may be more common than previously thought. Most cases were unilateral and diet restriction had no effect on frequency. The CrCd view was critical for diagnosis. Elbow OA was not directly associated with UME. Clinical Relevance—Infrequent diagnosis of UME could result from infrequent radiography and use of only the flexed lateral radiographic projection required by the Orthopedic Foundation for Animals for elbow screening. Like hip evaluations, screening for UME should be continued for life, until genetics are better understood. Lack of association between UME and elbow OA suggests that UME is not likely a component of elbow dysplasia.